The United Launch Alliance successfully tossed a new Global Positioning System satellite into position Friday night. The satellite is the seventh of twelve planned launches of interim satellites to refresh aging spacecraft and improve functionality of the GPS network.

Timelapse of the GPS IIF-7 launch off of Space Launch Complex 41 at Cape Canaveral Air Force Station, Florida late on Friday night. Image credit: ULA

The launch window started at at 11:23 pm Eastern time on Friday, August 1st. The window was open for 18 minutes, giving a tiny bit of grace for any minor issues that came up. Prior to launch, conditions were at 70% odds for favourable weather conditions, with some concern of anvil clouds, cumulus clouds, or a thick cloud layer. Happily, it was a smooth countdown and a beautiful night launch, successfully delivering the satellite into position and providing us with another batch of gorgeous launch photographs.

If the full launch video is too long, here's a much shorter mission-highlights reel:

To give you an idea of the beautiful complexity of orbital dynamics and rocket science, here's a breakdown of the intricate detail for every stage of the mission from launch to final separation: The first stage ignited at T-2.7 seconds, burning for 4 minutes, 3.6 seconds before being jettisoned 6 seconds later. The first stage carried the rocket from liftoff (T+1.1 seconds) all the way out of the atmosphere, with manoeuvring at T+17.2 seconds. At T+259.6 seconds (4 minutes, 19.6 seconds into the mission), the second stage ignited. The second stage burned for 12 minutes, 49.2 seconds, slipping into a parking orbit and coasting near the apogee of the target orbit for the satellite for just under 3 hours. By "Just under," I really mean, "0.4 seconds under," because that's the sort of number rocket scientists care enough about to not round!) At 3 hours, 17 minutes, and 47.2 seconds into the mission, the second stage started up again for a quick 2 minute, 8.4 second burn before cutting off. Finally, 4 minutes and 45.7 seconds later, the satellite separated from the rocket.

GPS IIF-7 arriving at Cape Canaveral Airforce Base in Florida in preparation for the launch. Image credit: US Air Force

Currently, 31 GPS satellites are in orbit, with IIF-7 bumping that number up to 32 once it gets declared fully operational. We only need 24 functional satellites for the Global Positioning System to work, but it's nice to have spares just in case something goes wonky. Considering GPS is a Department of Defense project and their largest constellation of satellites, "fully functional" is not an optional proposition, so they get all the spares they decide are necessary.

The current constellation of GPS satellites are all second generation satellites, but from various classifications of updates. Before today, the constellation had six GPS IIA satellites, twelve GPS IIR satellites, seven GPS IIRM satellites, and 6 GPS IIF satellites.
The earliest generation of still-functioning Global Positioning System satellites are GPS Block IIA, launched between 1989 and 1997. They're hitting the end of their designed 7.5-year lifespans, so are being replaced by a set of interim Block IIF satellites.

The GPS Block IIF satellites are interim class of satellites intended to provide service until the next generation of GPS Block IIIA are finalized, built, and make it into orbit. The Block IIIAs were originally intended to launch this year, but were delayed. They're currently projected to make orbit in 2016, assuming nothing else happens to push them back farther.

The Boeing-manufactured Block IIF satellites have a few of the new enhanced capacities that should result in greater accuracy, increased signal, enhanced performance (including an L5 signal for civilians), and improved resistance to jamming. Because they're being dropped directly into the target orbits, they also don't need the apogee sensors of earlier models. Between the improved technology and the reduced sensor load, the IIFs are a bit lighter, massing 1,630 kilograms (3,590 pounds). Despite their rather temporary-sounding classification, the interim Block IIF satellites have a 12-year operational lifespan, longer than the Block IIAs they are replacing.

An Atlas V blasting off with GPS IIF-7 on August 1, 2014. Image credit: ULA

The Block IIA satellites were lifted into orbit by Delta II rockets, which got them close enough but required additional manoeuvring to take up final positions in the satellite constellation. The newest block are being lifted by more powerful rockets capable of depositing them directly in their final orbits. Consequently, the Block IIF satellites don't need apogee sensors to get them into the appropriate positions, contributing to their reduced mass compared to earlier GPS spacecraft.

All the Block IIF satellites are being launched by United Launch Alliance (ULA). The first five satellites were launched by Delta IV rockets; IIF-6 in May and now IIF-7 were both launched by Atlas V rockets.

A Delta IV rocket at Cape Canaveral Air Force Station awaiting boosting the Global Positioning System IIF-6 satellite into orbit on May 16, 2014. Image credit: Air Force Space Command Public Affairs

This specific satellite will be filling slot 3 of the constellation's plane F. It'll be at an altitude of
20,460 kilometres (12,700 miles) at an inclination of 55 degrees, making a complete orbit every twelve hours. It's replacing GPS IIR-2 (USA-132), which launched in July 1997. Once IIF-7 proves itself fully capable, IIR-2 will slide on over to take on the role of operational reserve for plane F, relieving GPS IIA-5 (GPS II-16, USA-83), which launched way back in 1992.

The Global Positioning System is just one of several positioning satellite constellations currently in use. The other major global network is GLONASS, maintained by Russia. Several regional programs also exist, utilizing a smaller number of satellites to provide positioning data for specific regions.

The next GPS satellite scheduled for launch is IIF-8 in mid-October. It arrived at Cape Canaveral on July 16th to begin pre-launch preparations.

The Atlas V, serenely awaiting launch in the days leading up until August 1. Image credit: ULA